NVT ensemble: Difference between revisions
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The additional tags in the column for every thermostat have to be set. For example, the [[Nosé-Hoover thermostat]] needs the additional {{TAG|SMASS}} tag. To enforce constant volume throughout the calculation, set {{ | The additional tags in the column for every thermostat have to be set. For example, the [[Nosé-Hoover thermostat]] needs the additional {{TAG|SMASS}} tag. To enforce constant volume throughout the calculation, set {{TAG|ISIF|3|op=<}}. In NVT MD runs there is no control over pressure because the volume is fixed. The average value will therefore depend on the initial lattice given in the {{FILE|POSCAR}} file. It is often desirable to equilibrate the lattice degrees of freedom, for example, by running an [[NpT_ensemble|NpT simulation]] or by performing structure and volume optimization with {{TAG|IBRION|1 or 2}} and setting {{TAG|ISIF|2|op=>}}. A general guide for molecular-dynamics simulations can be found on the [[Molecular dynamics calculations|molecular-dynamics]] page. | ||
''Example {{FILE|INCAR}} file for the [[Nosé-Hoover thermostat]]'' | ''Example {{FILE|INCAR}} file for the [[Nosé-Hoover thermostat]]'' | ||
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== Footnotes and references == | == Footnotes and references == | ||
<references> | <references> | ||
<ref name="legacy-nh">If possible, use another Nosé–Hoover thermostat implementation, e.g. {{ | <ref name="legacy-nh">If possible, use another Nosé–Hoover thermostat implementation, e.g. {{TAG|MDALGO|2}}, see also comments [[MDALGO#MDALGO=0:_Standard_molecular_dynamics|here]].</ref> | ||
</references> | </references> | ||
[[Category:Molecular dynamics]][[Category:Ensembles]][[Category:Thermostats]] | [[Category:Molecular dynamics]][[Category:Ensembles]][[Category:Thermostats]] | ||
Latest revision as of 08:00, 24 October 2025
The NVT ensemble (canonical ensemble) is a statistical ensemble that is used to study material properties under the conditions of a constant particle number N, constant volume V and a temperature fluctuating around an equilibrium value [math]\displaystyle{ \langle T \rangle }[/math]. This page describes how to sample the NVT ensemble from a molecular-dynamics run.
Instructions for setting up an NVT ensemble
There are multiple choices of thermostats to control the temperature for the NVT ensemble: The stochastic Andersen thermostat, Langevin thermostat and CSVR thermostat, as well as the deterministic Nosé-Hoover thermostat, Nosé-Hoover chain thermostat and Multiple Andersen thermostats can be used. See table for the corresponding MDALGO setting and related tags.
| NVT ensemble | Nosé-Hoover[1] | Andersen | Nosé-Hoover | Langevin | Nosé-Hoover chain | CSVR | Multiple Andersen |
|---|---|---|---|---|---|---|---|
| MDALGO | 0 | 1 | 2 | 3 | 4 | 5 | 13 |
| additional tags to set | SMASS | ANDERSEN_PROB | SMASS | LANGEVIN_GAMMA | NHC_NCHAINS, NHC_PERIOD, NHC_NRESPA, NHC_NS | CSVR_PERIOD | NSUBSYS, TSUBSYS, PSUBSYS |
The additional tags in the column for every thermostat have to be set. For example, the Nosé-Hoover thermostat needs the additional SMASS tag. To enforce constant volume throughout the calculation, set ISIF < 3. In NVT MD runs there is no control over pressure because the volume is fixed. The average value will therefore depend on the initial lattice given in the POSCAR file. It is often desirable to equilibrate the lattice degrees of freedom, for example, by running an NpT simulation or by performing structure and volume optimization with IBRION = 1 or 2 and setting ISIF > 2. A general guide for molecular-dynamics simulations can be found on the molecular-dynamics page.
Example INCAR file for the Nosé-Hoover thermostat
#INCAR molecular-dynamics tags NVT ensemble IBRION = 0 # choose molecular dynamics MDALGO = 2 # use Nosé-Hoover thermostat ISIF = 2 # compute stress tensor but do not change box volume/shape TEBEG = 300 # set temperature NSW = 10000 # number of time steps POTIM = 1.0 # time step in femto seconds SMASS = 1.0 # setting the virtual mass for the Nosé-Hoover thermostat
| Mind: This INCAR file only contains the parameters for the molecular-dynamics part. The electronic minimization or the machine learning tags have to be added. |
Related tags and articles
Molecular-dynamics calculations, ISIF, MDALGO, LANGEVIN_GAMMA, SMASS,ANDERSEN_PROB, NSUBSYS, TSUBSYS, PSUBSYS